Rated 5 out of 5 stars

le Tomáš Maleček ar Lún. 27, 2015 ·

Has served me well up to Thunderbird 38, where the functionality is built in:

• Expanded Folder Pane columns in New in Thunderbird 38.0 support article:
https://support.mozilla.org/en-US/kb/new-thunderbird-38#w_expanded-folder-pane-columns
• “Show expanded columns in folder pane” in release notes:
https://www.mozilla.org/en-US/thunderbird/38.0.1/releasenotes/
• Bug 464973 in Bugzilla:
https://bugzilla.mozilla.org/show_bug.cgi?id=464973

Just check View → Layout → Folder Pane Columns.